This invention relates to the field of display systems, more particularly to display systems using multiple light sources in combination with a spatial light modulator projection system using a rod integrator.
Many new types of displays systems have been developed that use a spatial light modulator or light valve in combination with an illumination source to project an image. These display systems are capable of providing high resolution, high contrast images having an excellent color gamut. One of the key criteria consumers use to distinguish various display systems is the brightness of the image. High image brightness is critical in the marketplace. High image brightness enables viewers to clearly see the projected image, even in venues having a high ambient light level, and enables projection of very large images.
The brightness of the projected image is limited by the luminance, lumens per emitting area per solid angle, of the light source used in conjunction with the modulator. This is especially difficult to achieve with small light valves such as the digital micromirror device (DMD(trademark)). The DMD, which is less than an inch across, has a small etendue or area-solid angle product.
Arc lamps are very high luminance light sources, but are unacceptable for most display system applications because of their short lifetimes, generally less than 2000 hours. Other arc lamps, such as metal-halide lamps, have too large an arc to allow the lamp to be efficiently coupled to a small light valve such as a DMD. Because of the large arc, at 300-400 watt lamp may produce an image that no brighter than an image produced by a 100-150 watt small-arc lamp. A few arc lamps have both a long lifetime, between 6000 and 8000 hours, and a small etendue, but do not provide a high total flux. If these lamps can be combined, a display system could efficiently produce a high brightness image.
One technique that has been used to increase the brightness of a projected image is to use three lamps in combination with dichroic filters. The output of each lamp is filtered to provide a single primary colored light beam. The lamps sequentially are pulsed to peak the flux out of the lamp during a portion of the frame period. In concert, the three lamps act as a single sequential color source having a greater brightness than a single lamp. Unfortunately, pulsing the lamps reduces the stability of the arc and shortens the lifetime of the lamp.
What is needed is a long-life, high luminance, high flux light source that has a small etendue to enable efficient coupling to a small light valve.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention that provides a method and system for combining multiple light sources in light valve projectors. One embodiment of the claimed invention provides an illumination system comprised of a first and second lamp, and a first and second lens system. The first lamp for emits light along a first light path. The first lens system is comprised of a first and second cylindrical lens group on the first light path. An orientation axis of the second cylindrical lens group is perpendicular to an orientation axis of the first cylindrical lens group. The second lamp emits light along a second light path. The second lens system is comprised of a first and second cylindrical lens group on the second light path. An orientation axis of the second cylindrical lens group is perpendicular to an orientation axis of the first cylindrical lens group. The disclosed lens system allows the two light paths to be closely spaced and efficiently coupled to an integrating rod.
A second disclosed embodiment provides a display system using the an illumination system to efficiently couple two or more light sources to an integrating rod. The display system is comprised of: a first lamp for emitting light along a first light path, a first lens system comprised of a first and second cylindrical lens group on the first light path, an orientation axis of the second cylindrical lens group on the first light path being perpendicular to an orientation axis of the first cylindrical lens group on the first light path, a second lamp for emitting light along a second light path, a second lens system comprised of a first and second cylindrical lens group on the second light path, an orientation axis of the second cylindrical lens group on the second light path being perpendicular to an orientation axis of the first cylindrical lens group on the second light path, an integrating rod having an entrance face on the first axis and the second axis, the integrating rod capable of combining beams of light on the first and second light paths into a homogenous light beam traveling along a third light path, a controller for receiving one or more image signals and outputting data signals, and a light valve on the third light path operable to modulate the homogenous light beam in response to the data signals to form an image bearing beam of light.
The disclosed optical architectures enable two small-arc light sources to be used instead of one larger light source. The small-arc light sources have a much longer life and a solid angle that is more efficiently coupled to a small light valve such as a DMD.